Winding duct construction for power transformer

ABSTRACT

The ducts between adjacent layers of windings are formed into a plurality of longitudinal passageways of generally square cross section. A flat strip of insulating material twisted about the central longitudinal axis thereof is provided in each of the passageways to augment the heat flow from the winding to the coolant flowing in the passageway.

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336/60 Primary ExaminerThomas J. Kozma Attorneys-Paul A. Frank, John F.Ahem, Julius J.

Zaskalicky, Frank L. Neuhauser, Oscar B. Waddell and 54 WINDING nuc'rcous'muc'nou FOR POWER Jmph TRANSFORMER 8Claims,5DrawingFigs.

a1 twisted about the central lon vided in each of the pas llllllll fromthe winding to the coolant flowing in the passageway.

. 7 Hawaii n! PATEN-Tinumamn 3.579.162 sum 1M2 177 Van z; of) I WINDINGDUCT CONSTRUCTION FOR POWER TRANSFORMER WINDING DUCT CONSTRUCTION FORPOWER TRANSFORMER The present invention relates to forced convectioncooling systems for power transformers, and in particular, toimprovements in the structure of the cooling ducts in the windings ofthe transformer to augment the heat transfer from the windings to theliquid coolant circulated in the ducts.

A typical forced oil and forced air-cooled power transformer apparatusincludes a tank filled with insulating oil coolant, a power transfonnerimmersed in the fluid, and a cooler or radiator system having an inletend coupled to one end of the tank adjacent one end of the windings andan outlet end connected to the tank adjacent the other end of thewindings. The windings of the power transformer are provided with aplurality of ducts each generally rectangular shaped in cross sectionextending from one end of the windings to the other thereof and eachsituated between adjacent layers of the windings. A pump is provided tocirculate the oil coolant through the ducts and the cooler. A fan isprovided in the forced air-cooling circuit of the cooler to produceairflow over the cooler or radiator tubes thereof to remove the heatfrom the oil coolant. In such an arrangement as. described, good heattransfer is highly desirable between the windings and the oil coolantcirculating in the ducts as the oil coolant can be operated at atemperature closer to the temperature of the windings and hence thetransformer can be operated at a higher power rating. Such mode ofoperation with higher oil temperature also means that the cooler canoperate more efficiently in removing heat from the oil due to largertemperature gradients existing between the cooler tubes and thecirculated air currents.

The present invention is directed to the reduction in the thermalresistance between the windings and the cooling ducts of a transformerto decrease the temperature drop necessary to drive a given amount ofheat from the conductors of the winding to the coolant oil circulated inthe ducts.

Accordingly, an object of the present invention is to provide astructure for winding ducts of a power transformer for improving theheat transfer between the windings and the oil flowing in the ducts.

Another object of the present invention is to provide simple structureof low cost requiring a minimum of modification of existing ductstructures for decreasing the thermal resistance between the winding ofa transformer and the coolant flowing in the ducts.

In accordance with an illustrative embodiment of the present inventionas applied to a power transformer, there is provided a plurality ofpassageways in the ducts formed between adjacent layers of a winding ofthe transformer. In each of the passageways are provided a means forimparting a vortical motion to the coolant flowing therethrough. Oneform of such means is a flat insulating strip twisted about the centrallongitudinal axis thereof. The passageways are preferably generallysquare in cross section.

The novel features which are believed to be characteristic of thepresent invention are set forth in the appended claims. The inventionitself, however, together with further objects and advantages thereofmay best be understood by reference to the following description takenin connection with the accompanying drawings wherein:

FIG. 1 is a plan view of a power transfonner apparatus including a tankin which the transformer is included and a cooler or radiator connectedthereto for cooling the liquid coolant in which the transformer isimmersed;

FIG. 2 is a front view of the transformer apparatus of FIG. 1;

FIG. 3 is an enlarged sectional view of a winding of the transformer ofFIG. 2 taken along section lines 3-3 showing an embodiment of thepresent invention;

FIG. 4 is an enlarged developed view of a section of FIG. 4

, included in the indicated dotted enclosure thereof; and

FIG. 5 is a side view of the section shown in FIG. 4.

Referring now to FIGS. 1, 2 and 3, there is shown a tank containing aninsulating liquid coolant 11, such as oil, in which a powertransformerl2 is immersed. Associated with the tank for the purpose ofcooling the oil therein is a cooler 13. The inlet end 14 of the cooleris connected to an upper portion of the tank 10 adjacent one end of thetransformer 12 for receiving coolant that has been heated by powerdissipatedin the transformer. The outlet end 15 of the cooler, isconnected to the inlet endof a circulating pump 16, the outlet end ofwhich is connected to a lower portion of the tank 10 adjacent the otherend of the transformer. A ducting 17 is provided to channel the cooledcoolant from the pump l6'into the ducts located in the windings and coreof the transformer 12. The cooler 13 includes a plurality of radiatortubes through which the liquid coolant flows. A fan 20 is provided forforcing air or other suitable gaseous medium over the surface of thecooler tubes to remove the heat in the coolant flowing through thetubes. The power transformer 12 includes a core 21 and windings 22 and23. The core 21 includes a plurality of ducts 24, only one of whichis'shown, extending from one end adjacent the lower portion of the tankto the upper portion of the tank. Each of the windings 22 and 23includes a plurality of ducts 25, only one of which is shown in eachwinding between adjacent layers of the windings extending from one endto the other end thereof.

Reference is now made particularly to FIG. 3 which shows a sectionalview of winding 22 of the transformer taken along section line 3-3. Thewinding includes a plurality of layers only two of which, layers and 31,are shown. The layers 30 and 31 are maintained in spaced insulatingrelationship by a plurality of insulating spacers 32, for example, madeof wood or other suitable insulating material to provide a generallyrectangular shaped duct 25. Spacers 32 provide good mechanical supportbetween adjacent windings. Another group of insulating spacers 33provide a proper structural form to the duct 25, that is, they form aplurality of passageways 34, each of generally square cross section. The

- spacer 33 may be made of wood or of stacked paper insulation.

Referring now particularly to FIGS. 4 and 5 there are shown developedviews of a portion of the duct included in the dotted box 35 of FIG. 3.FIG. 5 shows an elevation view of the section of FIG. 4. Each element ofFIGS. 4 and 5 corresponding to elements of FIG. 3 has the same numericaldesignation. The duct 25 includes a plurality of the wide spacers 32preferably made of some material such as wood or plastic to provide goodsupport between adjacent layers 31 and 32 of the windings and alsoincludes aplurality of narrow spacers 33 located between the widespacers 32. The narrow spacers 33 may be made of wood or other suitablematerial such as paper. The narrow spacers are arranged to provide aplurality of generally square cross section passageways 34 in the duct25. In each of such passageways is located a thin flat strip ofinsulating material 36 twisted about the central longitudinal axis 37thereof and secured along the edge 38 or 39 thereof which is at points40 tangent to an adjacent spacer. If desired, the strip 36 may besecured to the ends of the passageway 34. The width of the strip 36 ismade. substantially equal to the side of the square passageway 34.Accordingly, the cylindrical surface representing the locus of thelongitudinal edges 38 and 39 of the strip 36 is tangent to the foursides of the square passageway 34 and encompasses a major portion of thevolume of the passageway.

In the operation of the transformer system, power generated anddissipated in the windings 22 and 23 of the transformer is cooled by theoil flowing in the ducts 25. The oil is moved through the passageways 34of the ducts by the action of the pump 16. The twisted flat strip 36located in each of the passageways imparts a vortical motion to the oilflowing therein. Such vortical motion has two principal actions inimproving the heat transfer from the windings 22 and 23 to the oilflowing in the passageways 34. The peripheral velocity of the vorticalflow in the passageway is greater than the mean flow of oil from one endof the other of the passageway. Ac-

cordingly, as oil is flowing more rapidly over the heat transfer surfaceof the windings and the passageways, a greater amount of heat istransferred to the oil bringing the fluid upto a temperature closer tothe temperature of the windings. The vortical motion also has the effectof forcing the heavier and cooler oil in the passageways to the walls ofthe passageways where it is most effective in removing heat from thewindings adjacent thereto. The vortical motion also has the effect ofremoving the hot oil from the vicinity of the heated walls of thepassageways. Accordingly, the net effect of the actions described is toraise the temperature of the oil flowing from the upper ends of thepassageways and the ducts of which they are a part. In addition, thevortical motion produces turbulence in the fluid flow which facilitatesand promotes heat transfer to the fluid from the windings. The hot oilflows into the inlet passageway of the cooler 13 where it is pumpedthrough the tubes of the cooler by the pump 16. The fan 20 forcesambient air over the tubes of the cooler 13 to remove the heattherefrom. As the arrangement of the present invention increases thetemperature of the oil applied to the inlet of the cooler 13 withoutraising the limit set for the winding temperature, improved powerhandling capability is obtained in the transformer system. in addition,as the cooler operates more efiiciently when the differential betweenthe oil temperature and the cooling air temperature is higher, thepresent arrangement achieves a more efficient cooling in the airflowsystem.

1 intend by the appended claims to cover all modifications that fallwithin the true spirit and scope of my invention.

What I claim as new and desire to secure by Letters Patent of the UnitedStates is:

I claim:

1. A forced convection cooling system for a former comprising:

a tank containing insulating liquid coolant,

a transformer immersed in said coolant, said transformer including awinding, said winding being in the fonn of a plurality of layers of wirehaving adjacent layers of said winding spaced to provide a plurality ofducts, each duct extending from one end of the winding to the other endpower transthereof,

a radiator system for said coolant having an inlet end connected to saidtank adjacent one end of said windings and having an outlet endconnected to said tank adjacent the other end of said winding,

pumping means connected in the fluid flow circuit including said ductsand said radiator system, and

each of said ducts including a plurality of passageways, each passagewayincluding means for producing a vortical motion in the fluid flowingthrough the passageway.

2. The combination of claim 1 in which said vortical motion producingmeans is a flat strip twisted about the central longitudinal axisthereof, the cylindrical surface representing the locus of thelongitudinal edges of said strip encompassing a major portion of thevolume of said passageway.

3. The combination of claim 2 in which each of said strips isessentially tangent to three sides of said passageway.

4. The combination of claim 2 in which each of said passageways issubstantially square in cross section and the width of said stripesbeing substantially equal to a side of said square.

5. The combination of claim 2 in which a plurality of insulating spacersextend along thelength of said winding in said duct to space one layerof said winding from an adjacent layer, said twisted tape being securedto one of said spacers at points of tangency therewith.

6. The combination of claim 5 in which said twisted tape is aninsulator.

7. A liquid-cooled power transformer comprising:

a winding, said winding being in the form of a plurality of layers ofwire having adjacent layers of said winding in spaced relationship toprovide a plurality of ducts extending from one end of said winding tothe other end thereof, each of said ducts including a plurality ofpassageways, each passageway including means for producing a vorticalmotion to the fluid adapted to flow therethrough. 8. The combination ofclaim 8 in which said ducts are oval in shape and in which saidpassageways are substantially square in cross section.

1. A forced convection cooling system for a power transformercomprising: a tank containing insulating liquid coolant, a transformerimmersed in said coolant, said transformer including a winding, saidwinding being in the form of a plurality of layers of wire havingadjacent layers of said winding spaced to provide a plurality of ducts,each duct extending from one end of the winding to the other endthereof, a radiator system for said coolant having an inlet endconnected to said tank adjacent one end of said windings and having anoutlet end connected to said tank adjacent the other end of saidwinding, pumping means connected in the fluid flow circuit includingsaid ducts and said radiator system, and each of said ducts including aplurality of passageways, each passageway including mEans for producinga vortical motion in the fluid flowing through the passageway.
 2. Thecombination of claim 1 in which said vortical motion producing means isa flat strip twisted about the central longitudinal axis thereof, thecylindrical surface representing the locus of the longitudinal edges ofsaid strip encompassing a major portion of the volume of saidpassageway.
 3. The combination of claim 2 in which each of said stripsis essentially tangent to three sides of said passageway.
 4. Thecombination of claim 2 in which each of said passageways issubstantially square in cross section and the width of said stripesbeing substantially equal to a side of said square.
 5. The combinationof claim 2 in which a plurality of insulating spacers extend along thelength of said winding in said duct to space one layer of said windingfrom an adjacent layer, said twisted tape being secured to one of saidspacers at points of tangency therewith.
 6. The combination of claim 5in which said twisted tape is an insulator.
 7. A liquid-cooled powertransformer comprising: a winding, said winding being in the form of aplurality of layers of wire having adjacent layers of said winding inspaced relationship to provide a plurality of ducts extending from oneend of said winding to the other end thereof, each of said ductsincluding a plurality of passageways, each passageway including meansfor producing a vortical motion to the fluid adapted to flowtherethrough.
 8. The combination of claim 8 in which said ducts are ovalin shape and in which said passageways are substantially square in crosssection.